The present invention relates to an electrode for determining the state of corrosion of metal reinforcement in concrete constructions, this being in the form of a wire that is more electro-positive than the reinforcement metal and that is surrounded by insulation. The electrically active part of the wire is in electrolytic contact with the moisture in the concrete.
In principle, corrosion protection for the reinforcement in concrete constructions is produced by the high alkalinity of the concrete, because of which a rust-inhibiting passive layer forms on the surfaces of the reinforcement steel. Despite this, in recent years, damage caused by corrosion has been identified in reinforced steel constructions, mainly in communications (road) infrastucture such as bridges, this having been caused predominantly by the effects of salt. Apart from the effects of salt, the passive layer on the surface of the steel can also be destroyed because the concrete reacts with the carbon dioxide in the surrounding air and thus loses its alkalinity by the formation of carbonates.
The potential on the boundary layer between the steel and the concrete can be measured with the help of electrodes. In time, a constant potential that corresponds to the passivated state of the reinforcement (area of passivity) is formed on the reinforcement, manufactured and installed in the normal way, which has undamaged corrosion protection. If there is a change in the state of the cement mortar, which can lead to corrosion, it will be possible to identify a reduction of the potential. This reduction is particularly great in the case of reinforcement steel in which there are places that are corroding.
An even more reliable estimate of the probability of corrosion can be achieved by measurement of the potential after anodic polarization. A brief anodic galvanostatic DC pulse is applied to the reinforcement steel through one of the measurement electrodes, and the resulting change in potential is measured. In a zone that is free of corrosion, there will be a greater change in potential than is found in a zone with areas of corrosion.
DD 72398 describes an electrode of the type described heretofore, in which the electrically active area lies uncovered in the concrete and only the connecting wire that leads outwardly therefrom is enclosed by continuous insulation. However, it is difficult to incorporate the secondary electrode that is used in the measurement process parallel and at a defined distance from the reinforcement steel, as is described in DD 72398. Even in the case of subsequently tightened wire anchors it is difficult to avoid metallic contact between the electrodes and the reinforcement steel with any degree of certainty. Of course, point contact between the electrodes and the reinforcement steel or extreme closeness of these two elements, which could falsify the results obtained, would be cause for concern if it was desired to install the measurement electrode in the concrete together with any reinforcement steel.